Photoflash lamp

ABSTRACT

A percussive-type photoflash lamp having an envelope comprised of a glass having a low coefficient of thermal expansion and a depending metal primer tube which is secured to the glass envelope by means of a graded seal having an intermediate expansion glass disposed between the envelope and the primer tube.

United States Patent [1 1 Audesse et al.

[ Nov. 13, 1973 1 i n0T0rLAsii LAMP [75] Inventors: Emery G. Audesse,Salem; Harold L. Hough, Beverly, both of Mass. [73] Assignee: GTESylvania Incorporated,

' Danvers, Mass.

[22] Filed: Oct. 2, 1972 [21] Appl. No.: 294,276

[52} U.S. Cl. 431/93 [51] Int. Cl. F21k 5/02 [58] Field of Search..431/93-95 [56] References Cited UNIT ED STATES PATENTS 3,535,06310/1970 Anderson et al. ..-43l/93 2,438,993 4/1948 De Boer 431/94FOREIGN PATENTS OR APPLICATIONS 667,689 ll/l938 Germany 431/93 PrimaryExaminer-Carroll B. Dority, Jr. Att0rneyNorman J. OMalley et al.

57 ABSTRACT A percussive-type photoflash lamp having an envelopecomprised of a glass having a low coefficient of thermal expansion and adepending meta] primer tube which is secured to the glass envelope bymeans of a graded seal having an intermediate expansion glass disposedbetween the envelope and the primer tube.

9 Claims, 2 Drawing Figures PATENTEU NOV 1 3 I973 PRIOR ART PHOTOFLASHLAMP BACKGROUND OF THE INVENTION This invention relates to themanufacture of pohotoflash lamps and particularly those of thepercussive Generally speaking a percussive-type photoflash lampcomprises an hermetically sealed, lighttransmitting envelope containingasource of actinic light and having a primer secured thereto. Moreparticularly, as described in U.S. Pat. No. 3,535,063, the percussiveflashlamp may comprise a length of glass tubing constricted to a tip atone end and having a coaxially disposed metal primer tube sealed in theother end. The glass tubing defines the lamp envelope and contains acombustible, such as shredded zirconium foil, and acombustion-supporting gas, such as oxygen. To complete the primerstructure, a wire anvil coated with a layer of fulminating material iscoaxially disposed within the primer tube. Typically, the envelope iscomprised of G-l type soft glass having a coefficient of thermalexpansion within the range of 85 to 95 X per C between C, and 300C, andthe primer tube is formed of a metal having a similar coefficient ofthermal expansion so as to provide a match seal.

Operation of the percussive type photoflash lamp is initiated by animpact onto the tube to cause deflagration of the fulminating materialup through the tube to ignite the combustible disposed in the lampenvelope and, thus, flash the lamp. During lamp flashing, the glassenvelope is subject to severe thermal and mechanical shock due to hotglobules of metal oxide impinging on the walls of the lamp. As a result,cracks and crazes occur in the glass and, at higher internal pressures,containment becomes impossible. In order to reinforce the glass envelopeand improve its containment capability, it has been common practice toapply a protective lacquer coating on the lamp envelope by means of adip process. To build up the desired coating thickness, and glass isgenerally dipped a number of times into a lacquer solution containing asolvent and a selected resin, typically'cellulose acetate. After eachdip, the lamp is dried to evaporate the solvent and leave the desiredcoating' of cellulose acetate, or whatever other plastic resin isemployed.

In the continuing effort to improve light output, higher performanceflashlamps have been developed which contain higher combustible fillweights per unit of internal envelope volume along with higher fill gaspressures. In addition, the combustible material may be one of the morevolatile types, such as hafnium. Such lamps, upon flashing, appear tosubject the glass envelopes to more intense thermal'shock effects, andthus require stronger containment vessels. One approach to this problemhas been to employ a hard glass envelope, such as the borosilicate glassenvelope described in U.S. Pat. No. 3,506,385, along with a protectivedip coating. More specifically, this patent describes an electricallyignitable lamp having in-leads of a metal alloy such as Kovarsecured byan internal expansion match seal in a glass envelope having acoefficient of thermal expansion in the range of 40 to 50 X 10" per C.Type 7052 glass is mentioned as typical. The patent imposes a minimum of40 X 10 per C on the coeffici-- ent of thermal expansion of the glass toassure the necessary match seal with the Kovar in-Ieads. Further, it istheorized that glass in this thermal expansion range provides a morebeneficial mode of fracture which results in a delay in crack time afterflashing. More specifically, fracture of the glass is delayed to a timewhen the pressure in the lamp has been reduced to a point wherecontainment is more readily assured.

As described in copending application Ser. No. 294,308, filed Oct. 2,1972, assigned to the present assignee, it has been discovered that byusing glasses having an even lower thermal expansion than that specifiedin the aforementioned U.S. Pat. No. 3,506,385 the flashlamp envelope canbe made even more resistant to thermal shock and thereby delay cracktime even further. Alternatively, the use of lower thermal expansionglass provides a lamp capable of higher thermal loadings, as the glasssurface stresses 0 are proportional to the thermal expansion a of theglass. In particular, we

have found that glasses having a coefficient of thermal expansion withinthe range of 30 to 40 X 10 per C between 0C and 300C are particularlysuitable for improving the containment offlashlamp envelopes.Hereinafter, such glass will be referred to as low-expansion glass. Ofcourse, fused quartz has a very low coefficient of thermal expansion, inthe order of 4 X 10' per C-, but it is somewhat costly for thisapplication.

In attempting to use a low-expansion glass envelope in theabove-described percussive flashlamp structure, however, a sealingproblem arises as the commercially suitable metals for the primer tubeall have a substantially higher coefficient of thermal expansion thanthe glass and, therefore, are not suitable for providing a match seal.More specifically, referring to the envelope primer assembly of FIG. 1,in the above-referenced prior art percussive flashlamp, the metal primertube 10 is secured to the glass envelope 12 by means of an internalexpansion match seal. If envelope 12 is formed of low-expansion glass(e.g., a glass having a thermal expansion of about 32 X 10 per C) andtube 10 is formed of a low thermal expansion metal alloy such as Kovar(having a minimum thermal expansion of about 45 X 10 per C), there willbe a mismatch between the mating materials and, upon cooling, the Kovarwill contract faster than the glass. In this event, tube 10 willcontinue to adhere to envelope 12, but the faster contraction ofthe'metaI will place the adjacent glass area under tension, asillustrated by the arrows. This results in an unacceptably weak sealarea, as the strength of glass is reduced in tension.

SUMMARY OF THE INVENTION 7 In view of the foregoing, it is an object ofthe present invention to provide a percussive-type photoflash lamphaving an improved containment vessel.

Another object of the invention is to provide an improved glass-to-metalseal for a percussive flashlamp.

A principal object is to provide a percussive-type photoflash lamphaving a low-expansion glass envelope, and a strong glass-to-metal sealbetween the envelope and primer tube.

These and other objects, advantages and features are attained, inaccordance with the invention, by sealing a body of intermediateexpansion glass between the low expansion glass'envelope of thepercussive flashlamp and the higher expansion metal primer tube. In apreferred embodiment, the glass envelope of the lamp has a meancoefficient of thermal expansion of about 32 X 10" per C between 0C and300C; the primer tube is formed of a metal alloy having a meancoefficient of thermal expansion of about 50 X 10 per C between 25C and300C; and the body of intermediate expansion glass comprises a pressedand sintered bead of glass having a mean coefficient of thermalexpansion of about 46 X 10* per C between C and 300C. This provides agraded seal between the metal tube and glass envelope which avoids thecreation of high stresses at the glass-to-metal interface and crackingof the seal.

BRIEF DESCRIPTION OF THE DRAWINGS This invention will be more fullydescribed hereinafter in conjunction with the accompanying drawings, inwhich:

FIG. 1 is an enlarged fragmentary cross-section illustrating theglass-to-metal seal of a prior art percussive flashlamp to whichprevious reference has been made; and

FIG. 2 is an enlarged sectional elevation of a percussive-typephotoflash lamp having a graded seal between the envelope and primeraccording to the invention.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to FIG. 2, a percussivelamp according to the invention comprises a length of glass tubingdefining an hermetically sealed lamp envelope 14 constricted at one endto define an exhaust tip 16 and having a primer 18 secured at the otherend thereof. Preferably, theglass of envelope 14 is selected to be alowexpansion glass, such as Corning Glass Works type 7070 hard glass,which has a mean coefficient of ther mal expansion of about 32 X 10 perC, between 0C and 300C, and a composition which is approximately: 71%SiO 1% A1 0 26% B 0 Li O, 0.5% Na o, and 1% K 0.

The primer 18 comprises a thin metal tube 20 which is closed at one end,a wire anvil 22 coaxially centered within tube 20, and a charge offulminating material 24 coated on the anvil. Tube 20 preferably isformed of a metal alloy such as that commercially known as Kovar, whichhas a mean coefficient of thermal expansion of about 50 X per C, between25C and 300C, and a composition which is approximately: 54% Fe, 29% Ni,17% Co, O.'5% Mn, 0.2% Si, and 0.06% C.

A combustible 26, such as filamentary zirconium or hafnium, and acombustion-supporting gas, such as exygen, are disposed within the lampenvelope, with the fill gas being ata pressure of greater than oneatmosphere. The exterior surface of the glass envelope 14 is coveredwith a suitable plastic coating, such as cellulose acetate.

The wire anvil 22 is held in place by a circumferential indenture 28which loops over the head 30, or other suitable protuberance, at thelower extremity of the wire anvil. Additional means, such as lobes 32 onthe wire anvil 22,-for example, may also be used instabilizing the wireanvil supporting it substantially coaxial within the tube and insuringclearance between the fulminating material 24 and the inside wall oftube 20. A deflector-shield 34, which may be a bead of refractorymaterial or formed of metal, is attached to the wire anvil just abovethe inner mouth of the tube 20.

Typically, the lamp envelope has an internal diameter of less thanone-half inch, and an internal volume of less than 1 cc., although thepresent invention is equally suitable for application to larger lampsizes.

Operation of the percussive-type lamp of FIG. I is initiated by animpact onto tube 20 to cause deflagration of the fulminating material 24up through the tube 20 to ignite the combustible 26 disposed within thelamp envelope.

In accordance with the invention, metal tube 20 is sealed in the end ofthe lamp envelope by means of a graded seal including a bead 36 ofpressed and sintered intermediate expansion glass. Preferably, bead 36is formed of a glass having a mean coefficient of thermal expassion ofabout 46 X 10 per C between 0C and 300C, such as Corning Glass Workstype 7050 glass, which has a composition of approximately 67% SiO 2% A10 24% B 0 and 7% Na O To provide a strong glass-to-metal seal, 7050glass powder is heated and pressed into a doughnut shaped preformcomprising the bead 36. This doughnut shaped bead 36 is then coaxiallylocated about tube 20 at its open end, and the assembly is rotated overthe flame of a torch to seal the glass bead 36 to the metal tube 20.Thereafter, the 7070 glass envelope 14 is sealed about the 7050 glassbead in the same manner. The choice of 7050 glass, with an expansion of46 is reasonably critical due to its suitable match to both the Kovartube 20, with an expansion of 50, and the 7070 glass envelope, with anexpansion of 32. The resulting graded seal avoids the creation of highstresses at the glass-to-metal interface and cracking of the seal.

Accordingly, a strong glass-to-metal seal is provided between alow-expansion glass envelope and the primer tube 20 to provide asignificantly improved containment vessel for a percussive flashlamp.More specifically, whereas the G1 type soft glass (expansion of 93) and7052 hard glass (expansion of 46) used on prior art flashlamps havethermal stress resistances of about 19C and 41C, respectively, thethermal stress resistance of 7070 glass (expansion of 32) is about 66C.By definition, thermal stress resistance of C is the temperaturedifferential between the two surfaces of a tube or constrained platethat will cause a tensile stress of 1,000 pounds per square inch on thecooler ufiace envelope of FIG. 2 provides a much higher resistance tothermal shock, thereby permitting greater loading of the lamp with acombustible material and oxygen to provide increased light output.

Although the invention has been described'with respect to a specificembodiment, it will be appreciated that modifications and changes may bemade by those skilled in the art without departing from the true spiritand scope of the invention.

What we claim is: I

1. A percussive-type photoflash lamp comprising:

an hermetically sealed glass envelope having a first mean coefficient ofthermal expansion;

a quantity of combustible material located within said envelope;

a combustion-supporting gas in said envelope;

a primer secured to and extending from one end of said envelope and incommunication therewith, said primer including a metal tube sealed insaid end of said envelope and having an exposed segment outside of saidenvelope, and a body of fulminating material located in the exposedsegment of said tube, said metal tube having a second mean coefficientof thermal expansion which is higher than said first mean coefficient;

and means for sealing said metal tube in said end of said envelopecomprising a body of glass sealed between said metal tube and saidenvelope and having a third mean coefficient of thermal expansion whichis intermediate said first and second mean coefficients.

2. A lamp according to claim 1 wherein said first mean coefficient ofthermal expansion is about 32 X per C between 0C and 300C.

3. A lamp according to claim 2 wherein said envelope is composed of aglass comprising the following constituents about in the proportionsstated by weight: 71% SiO 1% Al O 26% B 0 0.5% Li O, 0.5% Na O and 1% K0.

4. A lamp according to claim 2 wherein said second mean coefficient ofthermal expansion is about 50 X 10 per "C between C and 300C.

5. A lamp according to claim 4 wherein said metal tube is composed of ametal alloy comprising iron, nickel, and cobalt.

6. A lamp according to claim 4 wherein said third mean coefficient ofthermal expansion is about 46 X 10" per C between 0C and 300C.

7. A lamp according to claim 6 wherein said body of glass having saidthird mean coefficient of thermal expansion has a composition comprisingthe following constituents about in the proportions stated by weight:67% SiO 2% Al O 24% B 0 and 7% Na O.

8. A lamp according to claim 6 wherein said body of glass having saidthird mean coefficient of thermal expansion comprises a preformed beadof pressed and sintered glass powder, said bead being sealed about saidmetal tube, and said end of said glass envelope being sealed about saidbead.

9. A lamp according to claim 8 wherein said primer further includes awire anvil disposed within and substantially coaxial with said metaltube with said fulminating material being disposed thereon intermediatethe ends thereof, and a deflector-shield disposed on said anvilimmediately above the inner end of said tube.

1. A percussive-type photoflash lamp comprising: an hermetically sealedglass envelope having a first mean coefficient of thermal expansion; aquantity of combustible material located within said envelope; acombustion-supporting gas in said envelope; a primer secured to andextending from one end of said envelope and in communication therewith,said primer including a metal tube sealed in said end of said envelopeand having an exposed segment outside of said envelope, and a body offulminating material located in the exposed segment of said tube, saidmetal tube having a second mean coefficient of thermal expansion whichis higher than said first mean coefficient; and means for sealing saidmetal tube in said end of said envelope comprising a body of glasssealed between said metal tube and said envelope and having a third meancoefficient of thermal expansion which is intermediate said first andsecond mean coefficients.
 2. A lamp according to claim 1 wherein saidfirst mean coefficient of thermal expansion is about 32 X 10 7 per *Cbetween 0*C and 300*C.
 3. A lamp according to claim 2 wherein saidenvelope is composed of a glass comprising the following constituentsabout in the proportions stated by weight: 71% SiO2, 1% Al2O3, 26% B2O3,0.5% Li2O, 0.5% Na2O and 1% K2O.
 4. A lamp according to claim 2 whereinsaid second mean coefficient of thermal expansion is about 50 X 10 7 per*C between 25*C and 300*C.
 5. A lamp according to claim 4 wherein saidmetal tube is composed of a metal alloy comprising iron, nickel, andcobalt.
 6. A lamp according to claim 4 wherein said third meancoefficient of thermal expansion is about 46 X 10 7 per *C between 0*Cand 300*C.
 7. A lamp according to claim 6 wherein said body of glasshaving said third mean coefficient of thermal expansion has acomposition comprising the following constituents about in theproportions stated by weight: 67% SiO2, 2% Al2O3, 24% B2O3, and 7% Na2O.8. A lamp according to claim 6 wherein said body of glass having saidthird mean coefficient of thermal expansion comprises a preformed beadof pressed and sintered glass powder, said bead being sealed about saidmetal tube, and said end of said glass envelope being sealed about saidbead.
 9. A lamp according to claim 8 wherein said primer furtherincludes a wire anvil disposed within and substantially coaxial withsaid metal tube with said fulminating material being disposed thereonintermediate the ends thereof, and a deflector-shield disposed on saidanvil immediately above the inner end of said tube.